The role of a tank in dungeon runs is more like a shield. You're not so much clearing the enemies as you are just keeping their attention. One thing you'll want to get the hang of is positioning. From the sound of it, that may have been one problem in your Hall of Novice quest. While you have the enemy's attention, you'll want to try to have them facing away from the rest of the party. This way, if/when they use a big area skill, it's aimed at just you, and the rest of the party won't have to worry (though do be sure you step out of the way before you get hit too; those attacks can hurt). With other players, this isn't a huge problem for the early levels, as most players will be able to dodge if they need to, but obviously that archer NPC wasn't quite that bright (despite the fact that the Novice quests for all DPS teach you to avoid those area attacks...).Another skill you'll be developing is switching targets as you attack. While Flash does generate enmity to everything around you, you'll also want to make sure your attack combos switch to each enemy. This goes back to keeping their attention. Focusing too much on trying to kill one enemy could lead to another losing interest and attacking your party members.

As long as you've got the fundamentals down, all you should have to do is trust your healer to keep you alive, trust your DPS to kill things quick, while they trust you to keep them all safe.